1. Field of the Invention
The present invention relates to an apparatus for detecting whether a synchronous generator of a distributed power supply source, in a system where the distributed power supply source is able to cooperate with a commercial power system, has been separated from cooperation with the power system and has entered into what will be called isolated or single operation. The present invention also related to such a single operation detecting apparatus when the distributed power supply source includes both a synchronous generator and an induction generator.
2. Description of Related Art
Conventionally, a single operation detecting apparatus of this type detects the single operation of the distributed power supply by means of what will be called transfer breaking or by monitoring a voltage or frequency. These methods will be explained with reference to FIGS. 8A and 8B.
FIG. 8A is a block diagram showing a conventional single operation detecting apparatus. In FIG. 8A, reference numeral 10 designates a commercial power system whose generator 11 and a transmission line 12 are connected to a customer 20 through a system circuit breaker 13.
A synchronous generator 21 of the customer 20 is connected to the commercial power system 10 through a circuit breaker 22 for the synchronous generator and an interrupter or circuit breaker 23 on the side of the detection apparatus, so that the synchronous generator cooperates with the power system 10. A station service load 30 of the customer 20 is connected to the commercial power system 10 through a circuit breaker 31 for the station service load and the circuit breaker 23 for the detecting apparatus, as well as to the synchronous generator 21 through the circuit breaker 31 and the circuit breaker 22. Likewise, an external load 32 of the customer 20 is connected to the commercial power system 10 through a circuit breaker 33 for the external load, as well as to the synchronous generator 21 through the circuit breaker 23 and the circuit breaker 22.
The synchronous generator 21 of the customer 20 can be connected to the commercial power system 10 to operate in parallel with the commercial power system. The transfer breaking method can be used to detect when single operation begins. The single operation may be started when the system circuit breaker 13 of the commercial power system 10 is opened, and the synchronous generator 21 of the customer 20 is switched to the single operation mode from the mode of cooperation with the commercial power system 10. In this case, the circuit breaker 23 and the circuit breaker 33 are opened by a transfer breaking signal 14 from the commercial power system 10. This transfer breaking signal 14 can thus be used to detect when single operation of the generator 21 begins.
On the other hand, in the method for detecting single operation by monitoring the voltage or frequency, the voltage detected by a voltage detector 40 which is connected to the line system of the customer 20 as shown in FIG. 8A, or the frequency detected by a frequency detector 41, is supplied to a single operation detector 42. In other words, this method detects the single operation in a passive manner by monitoring variations in the voltage or frequency on the line system of the customer 20 by means of the single operation detector 42.
These conventional single operation detecting apparatuses, however, have the following problems. First, the method for detecting single operation by means of transfer breaking requires a dedicated line for transmitting the transfer breaking signal 14. This presents a problem in that a dedicated line with larger capacity will be demanded as the number of distributed power supplies increases in the future. In addition, using a shared line or radio for conveying the transfer breaking signal 14 is not practical and also not economical.
Second, the method for detecting single operation by monitoring the voltage or frequency has a problem in that it is impossible to detect such when no current flows between the commercial power system 10 and the customer 20 in the balanced state in which the total power consumed by the load of the customer 20, that is, the sum total of the external load 32 and the station service load 30, is balanced with the total amount of energy generated by the synchronous generator 21.
FIG. 8B illustrates a conventional single operation detection apparatus when the distributed power supply source includes more than a synchronous generator. In FIG. 8B, elements corresponding to those shown in FIG. 8A bear the same reference numbers and will not be further discussed.
In FIG. 8B, an induction generator 34 of the customer 20 is connected to the commercial power system 10 through an induction generator breaker 35 and the circuit breaker 25. The synchronous generator 21 and the induction generator 34 are operated in parallel by a known technique, and constitute a distributed power supply. An induction generator station service load 36 of the customer 20 is connected to the commercial power system 10 through a circuit breaker 37 for the service station load and the circuit breaker 25, as well as to the induction generator 34 through the circuit breaker 37 and the circuit breaker 35.
The induction generator 34 and the synchronous generator 21 of the customer 20 may be operated in parallel with the commercial power system 10. The single operation detection apparatus detects when the generators 21 and 34 are separated from the commercial system 10 and enter into the single operation mode. As in the arrangement shown in FIG. 8A, the transfer breaking method can be used to detect when single operation begins. The single operation mode may be started when the circuit breaker 13 of the commercial power system 10 is opened, and the induction generator 34 and the synchronous generator 21 of the customer 20 are switched into single operation and cease cooperating with the commercial power system 10. The circuit breaker 23 of the circuit breaker 35 of the customer 20 are opened by the transfer signal 14, which thus provides a way of detecting when single operation begins.
As was also the case in FIG. 8A, the voltage or frequency appearing on the line system of the customer 20 may be monitored to detect single operation of the generators 21 and 34. The voltage detector 40 or the frequency detector 41 may be used for this purpose with the output being supplied to the single operation detector 42.
The conventional arrangement shown in FIG. 8B suffers from the same problems that were discussed above with respect to FIG. 8A. Specifically, the method for detecting single operation by means of transfer breaking requires a dedicated line for transmitting the transfer breaking signal 14. This presents a problem in that a dedicated line with larger capacity will be demanded as the number of distributed power supplies increases in the future. In addition, using a shared line or radio for conveying the transfer breaking signal 14 would not be practical.
Moreover, the method for detecting single operation by monitoring the voltage or frequency has the problem that it is impossible to detect such when no current flows between the commercial power system 10 and the customer 20 under the balance state in which the total power consumed by the loads of the customer 20 (that is, the sum total of the external load 32, the induction generator station service load 36, and the synchronous generator service station load 32) is balanced with the total amount of energy generated by the induction generator 34 and the synchronous generator 21.